Nearly two out of three children ages one to four in the United States have been infected with SARS-CoV-2, according to a national analysis.1. Injuries in that age group increased more than at any other time during the Omicron wave, which the researchers say explains the variant’s high transmissibility.
The researchers looked for COVID-19 antibodies in blood samples from more than 86,000 children under the age of 18 — including about 6,100 children aged one to four years. In younger children, the number of infections doubled from 33% to 68% between December 2021 and February 2022.
Although the analysis included a small number of very young children, the results are consistent with the rapid rise in documented injuries in that age group, says Pamela Davis, MD, a medical researcher at Case Western Reserve University in Cleveland, Ohio.
Overall, the researchers found that most children ages 1-17 probably had the infection by February of this year. The incidence of infection in children aged 5 to 11 years was highest, 77%. Infection rates in children exceed those observed in adults (see ‘Omicron increase’).
These are important findings, particularly for low- and middle-income countries where vaccination rates are low among the adult population and where children likely have not been vaccinated for some time, says Fiona Russell, a pediatrician and infectious disease epidemiologist at the University of Melbourne in Australia. Immunity from infection can help prevent future infections and serious illnesses in children, but “the epidemic does not end until children are given a vaccination around the world.”
Reported cases of COVID-19 in the United States indicate that about 17% of children under the age of 18 are infected. “This is just the tip of the iceberg,” says Christy Clark, a medical epidemiologist at the US Centers for Disease Control and Prevention in Atlanta, Georgia, who led the study, which was published online this week without peer review. Reported cases, based on polymerase chain reaction (PCR) and antigen testing, do not significantly represent the true rate of infection, especially in children because many asymptomatic and mild infections may not have been tested.
To assess the magnitude of unrecorded infections, Clark and her colleagues looked for the presence of antibodies against SARS-CoV-2 in remaining blood samples taken during doctor visits between September 2021 and February 2022. The antibodies they looked for target a specific protein on the SARS-CoV-2 virus. That’s not found in the COVID-19 vaccines used in the US – so they can know that children have gained immunity to the infection, rather than being vaccinated.
The higher incidence rates among children are reflected in US hospitalization data. The number of children under five who were hospitalized with COVID-19 during the peak of the Omicron wave was 5 times that at the peak of the delta wave, and the number of those admitted to intensive care was 3.5 times higher.
Clark says many factors could explain the increased infection in young children and preschoolers, including that children under five are not eligible for vaccinations and may be less likely to wear masks or practice social distancing than older children and adults.
The numbers are staggering but not surprising, “and they may have underestimated the strength of the infection during the Omicron wave,” says Shabir Mahdi, a vaccinologist at the University of the Witwatersrand in South Africa. Antibody tests can’t tell if someone has been infected multiple times and may have missed some infection because antibody numbers decrease over time, he says. Madi says the antibody test used in the study captured only about 80% of infections that could be detected using a different antibody test.
Studies show that the risk of severe disease is lower in children with omicron than in delta. One American study2 By Davis and Rong Xu, a data scientist who also works at Case Western Reserve University, they looked at more than 650,000 children under the age of five and found that their risk of severe illness during an Omicron wave was about a third of that during a delta wave. , measured by emergency hospital visits between November 2021 and January 2022. Shaw says it will be important to consider the long-term effects of the boom in children.
Madi says hospitalization rates for children so far are much lower than those observed in older age groups. “The children were saved,” he says. “We should be thankful for that.”